Various exercise apparatus have been designed that enable exercisers to work against levers pivotally secured to a frame and coupled to resistance mechanisms. For example, exercise devices may include two levers that are operated by a user's legs while the user is in a standing position to simulate climbing exercise. Other devices may also include hand operable levers to simulate a full body climbing motion, or may include levers for simulation of rowing motion.
Often such exercise apparatus will include left and levers for exercising an exerciser's left and right limbs. The left and right levers are coupled for synchronous motion by a rope and pulley, teeter-totter mechanism, or other linkage. For such "dependent" action systems, often a single resistance device, such as a shock absorber, is coupled to just one of the levers. The lever linkage ensures that motion of the other lever is also resisted by the resistance device. The resistance against which the user must operate when moving either lever is altered by adjusting the single resistance device. Thus, adjustment of the resistance level is fairly simple. However, such dependent apparatus have the drawback of forcing the exerciser to exercise both sides of his or her body to the same extent, due to the linkage of the levers. Both levers must move through an equal range of motion, i.e., the levers are constrained to reciprocate in synchronous fashion. While desirable for some exercisers, other exercisers may prefer greater flexibility in tailoring the resistance against which the muscles of opposite limbs must work.
Other apparatus include left and right levers that are not linked together, and which are each coupled to separate corresponding resistance mechanisms. These "independent" action exercise devices enable each resistance mechanism to be separately adjusted. Such independent action exercisers also overcome another limitation of dependent exercisers by permitting the exerciser to operate opposing levers nonsynchronously. For example, an exerciser on an independent action climbing device may take a larger stride with one side of his or her body relative to the other side. This nonsynchronous motion is accommodated by the independent and separate resistance mechanisms. However, a drawback of these independent systems is that each resistance mechanism must be separately adjusted, making adjustment of the resistance level more time consuming. Further, those exercisers desiring to work each limb against the same level of resistance must ensure that both resistance mechanisms are adjusted to the same extent.